Tail lamps on vehicles have essentially a warning function, either when the vehicle is in movement or stopped. In addition, tail lamps also have a seduction function towards potential purchasers. Indeed, the aesthetics, shapes and colors proposed by designers play an important role in the commercial success of a particular vehicle. Auto makers and their research teams are thus eager for new technologies enabling them to create new styles for these tail lamps.
Interior and exterior glasses (here the term glass is used to denote the transparent or translucid material which forms part of the retroreflector, although it is not necessarily made of actual glass but may be manufactured from plastic) of the vehicle tail lights generally present at their surface optical elements. These optical elements redirect in a particular direction the light emitted by a light source which can be a bulb or LED. These optical elements are used for each of the functions of a vehicle, i.e., stop, back up, turn signal, tail lamps and fog lamps, and must meet the local regulations of the country in which the vehicle is to be commercialized.
These optical elements can take the shape of flute optics, small sized motifs or patterns that are juxtaposed and repeated many times, or any other geometry susceptible to deviate the path of a light ray in a particular direction (see FIG. 1).
These optical elements can be present on the exterior surface of the glass but also within glasses, closer to the light source. In such a case, reference will thus be made to lenses.
The materials used to mould these pieces are principally amorphous transparent plastics of the PMMA or PC type that are transformed by injection moulding. An injection mould is specifically designed for their production. The moulding of the optical elements is realized with the presence of one or more metallic inserts positioned within the mould cavity. These metallic inserts present a negative form of the optical element to be reproduced with a surface mirror.
It is also frequent in the fabrication of tail light manufacturing that multicolour moulds be used. The advantage of this process over monochromatic injection is the obtention in one single step of a polychromatic glass. Thus, on a same glass, signalling functions requiring different colors can be regrouped in a single piece.
Also, during the night, stopped vehicles are rendered visible to drivers of other vehicles due to the reflection of light. These light reflectors, the design of which is based on the principle of retroreflection within the catadioptric plastic prisms, are mandatory and the light signal is normalized. These plastic reflectors are formed from prisms having dimensions varying between 2 and 10 mm per side placed on the surface of the designated reflective zone.
A person skilled in the art will readily recognize that the manufacturing of a plastic reflector necessitates many fabrication steps. The manufacturing by plastic injection moulding on a matrix usually called electroform requires the realisation of metal prisms. The prisms are manufactured from metallic shafts or rods having a specific geometry, for example hexagonal. On these rods, three angled faces called reflection faces are machined, whose surface must have mirror properties. The angles of these faces are optimized in order to respond as much as possible to automobile lighting regulations. The dimension of these hexagonal prisms, most often, varies from 2 to 4 mm per side. Above 4 mm, these prisms are considered as large prisms. Once these prisms are manufactured, they are assembled with one another with junctions between them according to a given geometry dictated by the form of the signal lamp. Non reflecting optical elements may be inserted between the prisms. Once this assembly is realized, it is placed in an electrodeposition bath in order to obtain the negative of the assembled geometric form. This negative piece is called the electroform. It is the electroform that is placed in the injection mould. The role of the electroform is to permit to the plastic that will fill the mould to take the geometric shape of the assembly of the retroreflecting prisms obtained in the previous steps. Since the injected plastic is transparent (PMMA or polycarbonate), it permits light to travel within it and thus enables the faces of the prisms to reflect the light in the inverse direction.
In order to simplify the description of the present invention, optical elements includes optics and retroreflecting prisms described above.